Catheter based technology continues to grow rapidly as new innovative methods are developed to examine and treat areas once inaccessible without more invasive procedures. Much of the original motivation for this technology was to provide intravascular and cardiac catheters that could be used for cardiac diagnosis and interventions. Many specialized ones have been developed and are commercially available, and, as the technology has matured, these catheters have found more widespread use to areas of the body outside the thorax including the cranium and peripheral anatomy. Also, the catheters are not limited to blood vessels but may be used in other passages within the body.
Single function diagnostic catheters are now available to measure blood pressure, quantify blood velocity, and inject contrast dyes. More advanced diagnostic catheters image the internal physiology by optical or acoustical means. Specialized interventional catheters are in common use in catheterization laboratories today and perform procedures such as angioplasty, atherectomy, and stent placement. The most widely utilized catheter based method of imaging vessels is intravascular ultrasound (IVUS). Using ultrasound and a distally mounted transducer to generate echographic images during catherization procedures has a number of advantages over angiography. Furthermore, the location of the distal region or the catheter can be accurately determined using transducers of particular geometries; for example see Vilkomerson et al. U.S. Pat. No. 5,259,837.
Principles of IVUS involve using a sheath-catheter that is inserted into the vessel to be imaged. An intraluminal imaging catheter with at least one distally mounted ultrasound transducer is inserted into the sheath catheter. Generally there is either an array of stationary transducers (for examples see U.S. Pat. No. 9,417097 to Prodian et al. and U.S. Pat. No. 5,186,177 to O'Donell et al.) or a rotating transducer mounted at the distal end of the imaging catheter (U.S. Pat. Nos. 4,794,931 and 5,000,185 to Yock) to obtain full radial 2-dimensional images of the vessel. The intraluminal catheter is translated through the sheath catheter as 2-dimensional images are acquired. The images can be stacked to obtain a 3-dimensional image of the vessel under study.
The methods above assume that the imaged vessel has a linear shape introducing significant error into the constructed 3-dimensional images when the vessel imaged has curvature. In many catheterization procedures, it is highly desirable to have accurate, complete visualization of the total shape of the vessel or passage of interest including the longitudinal morphology or the curvature of the vessel. IVUS techniques described in the prior art that attempt to include vessel curvature use receiver transducers that are generally external to the body of the patient to receive the signals generated from the transducer or transducers of the intraluminal imaging catheter.
Difficulties associated with current IVUS techniques have been recognized and reported in several studies that attempt to do three-dimensional vessel reconstruction in tortuous vessel; see Prati et. al "Usefulness of On-line Three-dimensional Reconstruction of Intracoronary Ultrasound for Guidance of Stent Deployment", Am. J. Cardiol., Vol. 77, pp. 455-461, Mar. 1, 1996; Rosenfield et. al "Three-dimensional Reconstruction of Human Coronary and Peripheral Arteries from Images Recorded During Two-dimensional Intravascular Ultrasound Examination", Circulation, Vol. 85, pp. 1938-1956, November 1991; and Schwarzacher et. al "Impact of Curve Distortion Errors on Intravascular Ultrasound Measurements and Three-dimensional; Reconstruction" Am. J. Cardiol., Vol. 79, pp. 384-387, Feb. 1, 1997.
Another study examined the possibility of utilizing biplane angiography (fluoroscopy) to record vessel curvature while IVUS imaging was performed to visualize the vessel tissues; see Hans-Martin et. al "3D-surface reconstruction of intravascular ultrasound images using personal computer hardware and a motorized catheter control" Cardidovasc. Intervent. Radiol. Vol. 15, pp. 97-101, 1992. However, the method described is difficult to implement and subject to errors due the inability to precisely locate distal transducer region of the catheter within the vessel. Additionally, the use of angiography is difficult to interface with the current software and external hardware used in an ultrasound laboratory.
What is needed is an apparatus and method for detecting or measuring the curvature of vessels. The measuring device should not require additional external transducer receiver devices or additional external radiation sources. Additionally, the imaging apparatus should use ultrasound technology so that the imaging apparatus can be attached to existing ultrasound equipment. The apparatus should be simple so that it may miniaturized for imaging small vessel in the human body.